1. Field of the Invention
This invention relates to a flash fixing toner. More particularly, this invention relates to a flash fixing toner which excels in the flash fixing property and enjoys an economic feature of inexpensiveness.
2. Related Art
As a means to fix an image on a printing sheet or web in the electrophotographic process, the heat roll method has been mainly used conventionally. Since this method consists in causing a printing sheet such as of paper having an image formed with a toner thereon to be passed between hot rolls thereby thermally impressing the toner on the printing sheet, it incurs such problems as exposing the fixing part of a relevant device to the phenomenon of clogging, suffering the resolution to decline because the image is crushed, and imposing a limit on the kind of printing sheet or web.
The flash fixing method is one version of the noncontacting fixing method and is an excellent fixing method free from such problems of the heat roll method as mentioned above. Since this method barely enables the toner to be fused and fixed by relying on some of the components of the toner to absorb the light, particularly the infrared light, of a xenon flash lamp, however, it incurs defective fixing with a color toner which uses mostly a coloring agent having no or only sparing ability to absorb the infrared light.
As a means to solve the problem of defective fixing, JP-A-63-161,460 proposes a concept of having a flash fixing toner incorporate in a dispersed state therein an infrared absorbent showing peaks of light absorption at wavelengths of 800-1100 nm.
JP-A-60-57,858, JP-A-60-63,546, and JP-A-61-132,959 propose a concept of having a toner composition incorporate therein a specific compound showing peaks of light absorption at 800-1100 nm in an amount in the range of 1 wt. %-10 wt. %.
JP-A-03-48,585 discloses a discovery that a phthalocyanine compound having an aliphatic polyaminoammonium or a substituted guanidium ion at the terminal thereof is usable as an energy absorbent in a flash fixing toner.
The toner disclosed in JP-A-63-161,460 is not only inefficient but also unfavorable economically because the infrared absorbent is retained in a dispersed state in the binding resin and, consequently, the amount of the infrared absorbent to be incorporated in the binder is inevitably increased for the purpose of enabling the binding resin to be thoroughly fused by the heat-generating action of the infrared absorbent of this nature. Further, this increase in the amount of addition incurs the problem of affecting the tint of the toner and affecting the charging property. If the amount of the infrared absorbent to be incorporated in the dispersed state is unduly small, it will become necessary to heighten the energy of flash irradiation because no sufficient heat is generated and the fixing occurs only partly or deficiently. If the energy of flash irradiation is heightened as required, the temperature of the locally generated heat rises possibly to the extent of exposing the infrared absorbent itself and the binding resin as well to thermal decomposition and causing the occurrence of voids in the fixed image.
The toners disclosed in JP-A-60-57,858, JP-A-60-63,546, and JP-A-61-132,959 incur the problem of causing color pollution with the infrared absorbent because the amount of the infrared absorbent to be incorporated is relatively large similarly in the toners mentioned above and further because the compound cited as a concrete example is a substance showing only small absorption in the visible region and yet having a dark tint. Further, on account of the structure of the composition and the functional group thereof, the toners incur the problem of the ability to charge the toner.
The phthalocyanine compound disclosed in JP-A-03-48,585 is deficient in the solubility to be manifested to the binding resin which is used in the flash fixing toner. When this phthalo-cyanine compound is elected to be added as an infrared absorbent to the flush fixing toner, the amount of addition is necessarily increased so much as to incur the aforementioned problem of affecting the tint and the ability to charge and also incur the problem of the degradation of the resistance to the environment by the hydrophilic group at the terminal.
The flash fixing toners which are disclosed in the prior patent publications mentioned above are invariably obtained by the pulverizing method.
The pulverizing method does not easily produce a toner which are formed of particles of small diameters. The toner is amorphous morphologically and is deficient in flowability. As a result, the toner cannot fully manifest the feature of the flash fixing which resides in forming an image with high resolution.
Further, the dispersion of the infrared absorbent does not deserve to be called fully satisfactory because no special consideration is paid to the dispersion of the infrared absorbent. For the purpose of ensuring thorough fusion of the binding resin by the heat generating action originating in the absorption of light by the infrared absorbent, therefore, the amount of the infrared absorbent to be added is inevitably increased to the extent of rendering the production of the toner inefficient and uneconomical.
Besides, the increase in the amount of addition also incurs the problem of suffering the tint of the infrared absorbent to pollute colors and the structure of the relevant compound and the functional group thereof to affect the charging property as well.